The present invention concerns a method and a power generator installation for recovering thermal energy in the supercharging combustion-supporting air of a reciprocating internal combustion engine by means of a heat exchanger in which a heat-transfer fluid flows and for transferring thermal energy recovered by this fluid to a unit consuming thermal energy.
"Internal combustion engines" are typically:
gas turbines (aircraft engines, generator sets, etc), PA1 compression ignition engines (diesel engines, high-pressure gas engines, etc), and PA1 controlled ignition engines (petrol engines, low-pressure gas engines, etc). PA1 detecting the temperature of the supercharging air upstream of the heat exchanger; and PA1 if the temperature detected is less than a first set point temperature, short-circuiting the heat exchanger and heating the heat-transfer fluid approximately to the set point temperature by means of an auxiliary heating device.
The latter two categories are sometimes grouped together under the generic name "reciprocating internal combustion engines" which therefore designates internal combustion engines with ignition (compression ignition or controlled ignition).
The invention applies more particularly, although not exclusively, to diesel engines. It may be applicable in the future to petrol engines.
Document FR-A-2.353.715 describes a diesel engine power unit for ships supercharged by at least one turbo-compressor unit the compressor of which is connected by a pipe to a combustion-supporting air intake of the engine and the turbine of which is connected to an engine exhaust gas collecting pipe. A lost heat recovery boiler is disposed at the outlet of the exhaust gas turbine and its function is to heat and to vaporize a working fluid that produces mechanical energy in at least one steam turbine driving a device for increasing the pressure or the flowrate of the air directed to the air inlet of the engine and, where applicable or as an alternative, producing electrical energy.
This unit is characterized by a heat exchanger mounted in the air intake pipe of the engine through which flows a heat-transfer liquid intended to transfer at least some of the heat produced by compressing the supercharging air to a heat exploiting unit mounted in the ship.
A cooler mounted downstream of the heat exploiting unit on the heat-transfer liquid circuit or between the heat exchanger and the engine on the air intake pipe of the latter has the function of reducing the temperature of the heat-transfer liquid to a value enabling the supercharging air to be cooled to a value suitable for its entry into the motor in use.
When a large quantity of recovered heat is required at a high temperature, in the order of 130.degree. C. and above, a heat exchanger of the above kind can be difficult to use in the above manner. The compression ratio of the compressor of a supercharged engine varies with the instantaneous engine load and the air temperature at the exit of the compressor is then too low, in all circumstances and in particular when the engine is no longer operating at a very high load.
Where temperature levels of the above kind are required, it is routine practise to recover the heat in the exhaust gas by means of a boiler similar to that described in the document FR-A-2.353.715 mentioned above. The temperature of the exhaust gases is such that steam is used as the heat-transfer fluid in a boiler of the above kind, in order to minimize the size of the heat exchangers at the level of the heat consuming devices. Although widely used, this technique is difficult to use, the boiler and any control mechanisms being exposed to attack by the exhaust gases (high temperatures, thermal shock, variable loads, corrosion, insulative deposits). Furthermore, the heat-transfer fluid (steam) requires rigorous treatment which the operator is not always in a position to assure.
Consideration has also been given to providing these temperature levels by cooling the hot parts--engine block, cylinders, for example--of an internal combustion engine using a pressurized fluid, for example water, at a high temperature (in the order of 120.degree. C. to 130.degree. C.), so making available a large quantity of heat at a high temperature. Although a system of this kind has advantages, in particular with regard to the dimensions of the heat exchangers, it has a number of disadvantages such as a longer warm-up time, a longer run up to load after a cold start, and a higher temperature of the component parts of the combustion chamber and therefore a higher sensitivity to thermo-mechanical stresses and to corrosion. Moreover, a system of the above kind requires the use of additional devices to protect personnel. As a result systems of the above kind have until now been reserved to prototype installations and to temperature levels hardly exceeding 130.degree. C.
An aim of the present invention is to overcome these drawbacks.
To this end it proposes a method of recovering thermal energy in the supercharging combustion-supporting air produced by the combustion-supporting air compressor of an internal combustion engine wherein thermal energy is taken by means of a heat exchanger in which a heat-transfer fluid flows and which is situated on the combustion-supporting air circuit between the compressor and the engine and thermal energy recovered by the fluid is transferred to a thermal energy consumer unit, characterized in that it further consists in:
In the following, the term "heat-transfer" fluid or liquid is sometimes referred to as a "heat-conducting" fluid or liquid.
Using a process of the above kind makes available some of the heat lost during the operation of an internal combustion engine, at a high temperature, in practise 130.degree. or above, and without the drawbacks associated with recovering heat by means of the prior art devices described hereinabove.
In practise, with modern full load compression ratios, the temperature of the air leaving the compressor can be 200.degree. C. or more. This is why, in a preferred embodiment, the temperature of the heat-conducting fluid is further detected at the exit of the heat exchanger and, if the temperature detected exceeds a second set point temperature, the temperature of the heat-conducting fluid is reduced by passing at least some of it through an exchanger-cooling device in which a cooling fluid flows.
In this way it is possible to maintain the temperature of the heat-conducting fluid within a given temperature range or at a predetermined set point temperature if the second set point temperature is chosen to be equal to or similar to said first set point temperature.
In accordance with one particular aspect of the present invention, the consumer unit is the main cooling circuit of a second internal combustion engine and the second internal combustion engine is heated by transferring thermal energy from said heat-conducting fluid to this main cooling circuit.
This particularly beneficial feature of the present invention makes full use of the heat recovery possibilities when one or more engines operating at high power co-exist with one or more other engines that are stopped, warming up or running at low load.
For implementing the thermal energy recovery process as defined hereinabove, the present invention also proposes a power generating installation in which thermal energy is recovered from the supercharging air of an internal combustion engine, comprising an internal combustion engine, a compressor supplying combustion-supporting air to the engine via a combustion-supporting air supply line, a heat exchanger in which a heat-conducting fluid is circulated by pump means and which is disposed on said supply line, a consumer unit consuming thermal energy recovered by the heat-conducting fluid, communicating with the outlet of the heat exchanger via a hot heat-conducting fluid transfer line and with the inlet of the heat exchanger via a heat-conducting fluid return line, characterized in that it includes first means for detecting the temperature of the supercharging air upstream of the heat exchanger, a short-circuit line connected to the return line and to the transfer line, distributor means for distributing the heat-conducting fluid between the heat exchanger and the short-circuit line and an auxiliary heating device connected to the transfer line, and control means such that, if the temperature detected by the detecting means is less than a set point temperature, the distributor means short-circuit the heat exchanger via the short-circuit line and the auxiliary heating device heats the heat-conducting fluid approximately to the set point temperature.
An installation of the above kind achieves substantial savings compared to the cost of a heat recovery boiler using the exhaust gases (in practise more than 20%) because it has a simpler structure and is clearly more reliable and less bulky than any such boiler.
To be able to regulate the temperature of the heat-conducting fluid in a given temperature range, or to maintain this temperature at a predetermined value, in one preferred embodiment the installation further includes second means for detecting the temperature of the heat-conducting fluid at the outlet of the heat exchanger, a heat-conducting fluid exchanger-cooling device in which a cooling fluid flows and which is disposed on the return line downstream of the distributor means, a branch circuit communicating with the return line so as to short-circuit the exchanger-cooling device connected to the return line upstream of the exchanger-cooling device by second distributor means controlled by the control means so that, if the temperature detected by the second detecting means exceeds a second set point temperature, at least some of the heat conducting fluid is caused to flow through the exchanger-cooling device so that its temperature is reduced.
To simplify as much as possible the structure of the installation of the present invention and consequently to reduce the costs of the installation, the exchanger-cooling device is fluidically connected to the main cooling circuit of the internal combustion engine and/or to a heat exchanger for cooling the supercharging air disposed downstream of the heat exchanger on the combustion-supporting air supply line.
This has the advantage of exploiting the presence of cooling circuits that exist as standard on internal combustion engines.
The energy consuming unit can be an auxiliary heat exchanger adapted to transfer the recovered thermal energy over the transfer line to a heater, such as an lub-oil heater for heating the lub-oil prior to centrifuging or a fuel heater for heating the fuel prior to centrifuging and prior to injection into the engine.
The heat-conducting fluid can be superheated water, for example.
For safety reasons, in one preferred embodiment, the consumer unit is disposed between a hot manifold and a cold manifold providing an expansion tank and fluidically connected to the hot manifold via a discharge line on which is disposed a discharge valve.
Advantageously, the exchanger for cooling the supercharging air has two stages, namely a "high temperature" stage connected to the main cooling circuit of the internal combustion engine and a "low temperature" stage connected to a circuit having a lower exchange temperature.
Said heat exchanger-recovery device, the "high temperature" stage and the "low temperature" stage can therefore be disposed in series on the combustion-supporting air circuit and constitute a compact assembly disposed between the supercharging air compressor and the engine.
This system with three air cooling stages provides an economical way of cooling the combustion-supporting air to the very low temperature required by the engine when a cold source of limited capacity is available, whilst benefiting from the advantages of the invention.
In a variant, the installation includes a second internal combustion engine equipped with a main cooling circuit on which is mounted a heat exchanger adapted to receive thermal energy conveyed by said heat-conveying fluid to heat the second internal combustion engine.
By virtue of the above arrangements it is possible to preheat the second internal combustion engine when stopped or to warm it up using thermal energy recovered from said internal combustion engine that is running.
An installation of the above kind is naturally not limited to the use of two engines.